JP2003500323A - Nitrous oxide purification method - Google Patents

Abstract

  (57) [Summary] By supplying nitrous oxide gas and a reducing agent to a deoxidizing reactor, and by limiting the amount of nitrous oxide removed from the nitrous oxide gas, the reducing agent is reacted with oxygen using a catalyst to form a suboxide. A method for purifying nitrous oxide gas by greatly reducing oxygen in nitrogen gas.

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to a method for purifying nitrous oxide gas by removing various impurities.

BACKGROUND OF THE INVENTION Numerous methods are known in the art for purifying gaseous waste and exhaust gases from a variety of thermal power plants. These gases are NOx (NO,
_{N 2 O 3, NO 2,} N 2 O 4, N nitrogen oxides including 2 _{O 5)} and containing the undesired compounds, such as sulfur oxides. These methods are based either on the absorption of such impurities by liquid absorbents or their conversion (reduction) to innocuous compounds such as steam and nitrogen in the case of NOx reduction. The most widely used methods for NOx reduction use ammonia and selective catalytic reduction (SCR). The SCR method makes it possible to carry out the reduction of NOx to elemental nitrogen and water vapor in the presence of oxygen contained in gaseous waste. US Pat. No. 5,401,479
No. 4,859,439, 4,855,115, 4,789,533, 4
, 438,082, 4,720,476, 4,695,438, 4,73
2,743, 4,975, 256, 4,521, 388, 5,401, 4
78, and 5,753,582. The subject matter of all of these patents is incorporated herein by reference. After purifying small amounts of impurities in the gaseous waste by conventional methods / apparatus, the gaseous waste is discharged to the atmosphere.

Further, methods are known for purifying various industrial grade gases such as inert gases. For example, in US Pat. No. 4,579,723, CO, CO ₂ , H ₂ , H ₂ O and O ₂ are removed from argon gas using a multi-step catalytic method.
All of the subject matter of this patent is incorporated by reference.

Various methods have been used to remove O ₂ from very pure nitrous oxide gas resulting from independent industrial processes for later use in semiconductor fabrication. In JP 06-016402, a manganese oxide catalyst is used to remove oxygen from commercially produced nitrous oxide. However, oxygen is removed by using the oxygen present in the gas to oxidize the catalyst from lower to higher manganese oxides, which is easily removed by involving an oxygen-containing gas. It does not include the catalysis involved in the reaction that produces the said product.

So far, the removal of impurities from nitrous oxide gaseous waste has not been considered. Although the emission of nitrous oxide gaseous wastes to the environment is a source of pollution, nitrous oxide can be provided by economically and viablely separating these gaseous wastes to provide a source of industrial-grade nitrous oxide. The nitrogen waste becomes available for various processes, such as for use in the conversion of benzene to phenol by hydroxylation. U.S. Pat. Nos. 4,982,013, 5,001,280, 5,055,623,
5,110,995, 5,672,777, 5,756,861 and 5
, 808,167. All of the subject matter of these patents is incorporated by reference. Therefore, there is a need in the chemical industry for a method of purifying nitrous oxide gaseous waste while simultaneously producing commercially and economically suitable nitrous oxide for a variety of industrial applications.

DISCLOSURE OF THE INVENTION The present invention limits the supply of nitrous oxide gas and a reducing agent or precursor thereof to a deoxidation reactor and the amount of nitrous oxide removed from nitrous oxide gas. However, in order to reduce the oxygen in the nitrous oxide gas, deoxidation is carried out by reacting the reducing agent or its precursor with oxygen using a catalyst to make it an inactive substance, thereby reducing the amount of nitrous oxide. Purification method

Accordingly, the present invention provides for supplying nitrous oxide gas and ammonia or its precursor to a reactor system, and reacting ammonia or its precursor with NOx in nitrous oxide using a selective catalytic reduction catalyst. By performing a selective catalytic reduction, feeding hydrogen or its precursor to the reactor system, and reacting hydrogen or its precursor with oxygen in the nitrous oxide gas using a deoxidation catalyst. The present invention relates to a method for purifying nitrous oxide gas by performing deoxidation.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in Examples I and II, along with a description of exemplary embodiments below.
A more clear understanding can be had by reference to the accompanying drawings, which represent the data obtained as a result of the embodiment of the method according to the invention as described in.

Description of Illustrative Embodiments In accordance with the present invention, a catalytic process is used to purify nitrous oxide gas to provide an economical source of nitrous oxide suitable for a variety of commercial applications. Further, the method of the present invention removes nitrous oxide gaseous waste while maintaining the amount of nitrous oxide in the gaseous waste by selectively reacting selected impurities in the nitrous oxide gaseous waste. Selectively purify. Such purified nitrous oxide gaseous waste is disclosed in US Pat. No. 4,982,013,
5,001,280, 5,055,623, 5,110,995, 5,6
It can be utilized for the one-step hydroxylation of benzene to phenol, as described in 72,777, 5,756,861 and 5,808,167. The subject matter of all of these patents is incorporated herein by reference.

In one embodiment of the invention, nitrous oxide gaseous waste is passed through an SCR reactor in the presence of ammonia or its precursors to remove NOx (eg, by reacting), At the same time it does not reduce the amount of nitrous oxide in the gaseous waste. The reactor comprises at least one catalyst bed and of any suitable structure such as a fixed bed reactor (eg metal reactor, parallel plate reactor, ceramic honeycomb reactor, tumbler reactor, or lateral flow reactor). ) Can be. Preferably the reactor is a lateral flow reactor. In a lateral flow reactor, pellet type catalysts can be used in the fixed bed, and as a result, high contact efficiency can be provided with lower pressure drop than when honeycomb catalysts are also used. Homogeneous mixing between ammonia vapor and process gas is achieved by using a perforated plate.

The catalyst is a traditional metal such as Ti, V, W, Mo, Mn, Cu, Fe, C.
Includes all known NOx reducing SCR catalysts such as those based on r, Co, Ni, Zn, Sn, etc. The metal may be in the form of oxides, silica and / or
Alternatively, it may be incorporated into or placed on a conventional carrier such as alumina. Preferably, an oxide of Ti-V catalyst is used.

The catalyst pellets may be molded into any shape such as pillars, spheres, discs, rings, etc., or may be in the form of honeycomb blocks and can be used under normal SCR conditions. These conditions include the space velocity of the catalyst, its operating temperature, and N
It depends on the amount of Ox processing.

For example, ammonia or its precursor is 0.1 to 2.0 with respect to NOx,
The NO ratio is preferably 0.5 to 1.5, more preferably 0.8 to 1.2.
It is mixed with nitrous oxide gaseous waste containing x. Mixing is 100 ℃ ~ 600 ℃
, Preferably 120 ° C to 400 ° C, more preferably 150 ° C to 300 ° C. For the use of adipic acid gas waste that should maintain nitrous oxide,
The low temperature range between 50 and 350 ° C. is preferred. It is possible to use a space velocity in the range of 300 to 100,000 h ⁻¹ (amount of gas in cubic meters passing through one cubic meter of catalyst (apparent amount of catalyst layer) per hour, which is indicated by a dimension of reciprocal time). it can. This method can be performed under any pressure. However, suitable pressures range from about 1 to about 10 atmospheres.

Ammonia or its precursors are reacted with NOx to produce N ₂ and H ₂ O. Nitrous oxide present in the reactor is less than 200 ppm, preferably 40 p
It contains less than pm, more preferably less than 10 ppm NOx.

Ammonia and carrier gas are mixed prior to entering the reactor. The carrier gas can include any inert gas that does not significantly deactivate the catalyst. For example,
The carrier gas can include steam, hydrogen, argon, etc., or mixtures thereof. Preferably the carrier gas comprises steam.

In another embodiment of the invention, the nitrous oxide gaseous waste is passed through at least one reactor in the presence of a reducing agent or its precursor and a catalyst to be present in the gaseous waste. Oxygen and other impurities such as organic substances (such as CO) are removed without reducing the amount of nitrous oxide formed. The reactor contains at least one catalyst bed and can be of any suitable structure such as a fixed bed, tumbler reactor, or lateral flow reactor. Preferably the reactor is a fixed bed reactor.

The catalyst can include any known oxidation catalyst, such as those based on precious metals or combinations of precious metals such as platinum or palladium. The catalyst may be incorporated or placed on a conventional support such as silica and / or alumina. Preferably the catalyst is palladium metal with an alumina support.

The catalyst can be formed into any shape such as a column, a sphere, a disk, a ring, or a honeycomb block shape. Preferably, the catalyst is honeycomb block shaped.

In this embodiment of the invention, a stoichiometric amount of reducing agent or precursor thereof is
Mix with oxygen-containing nitrous oxide gaseous waste. This mixture is 0 ℃ ~ 600 ℃
, Preferably 5 ° C to 300 ° C, more preferably 10 ° C to 200 ° C. It is possible to use a space velocity in the range of 300 to 100,000 h ⁻¹ (amount of gas in cubic meters passing through one cubic meter of catalyst (apparent amount of catalyst layer) per hour, which is indicated by a dimension of reciprocal time). it can. This method can be performed under any pressure. However, suitable pressures range from about 1 to about 10 atmospheres.

The reducing agent or its precursors can be mixed with the nitrous oxide gaseous waste prior to entering the reactor or in the reactor. This can be accomplished using conventional means such as an in-line mixer. Suitable reducing agents include agents that selectively react with oxygen in nitrous oxide gaseous waste without reducing nitrous oxide in the gaseous waste. For example, the reducing agent can be hydrogen, which selectively reacts with oxygen present in the gaseous waste (using the appropriate catalysts described herein) to produce water. In embodiments of the present invention, it has been surprisingly found that hydrogen does not significantly reduce nitrous oxide in gaseous waste (hydrogen can also react with nitrous oxide to produce nitrogen and water). Expected). Another suitable reducing agent is, for example, carbon monoxide, which selectively reacts with oxygen without reducing the nitrous oxide present in the gaseous waste to produce carbon dioxide. The reducing agent can include a mixture of hydrogen and a gas such as carbon monoxide. Preferably, the reducing gas is a hydrogen containing gas. Hydrogen can be provided in any form, including any hydrogen-containing gas such as hydrogen, such as power plant gaseous waste, gaseous waste from dehydrogenation processes (eg, ethylbenzene to styrene). Preferably hydrogen is supplied in the form of pure hydrogen.

In another embodiment of the invention, the nitrous oxide gaseous waste is passed through an SCR reactor to remove NOx utilizing the NOx reduction process of the present invention, after which the nitrous oxide gaseous waste is removed. Once through the deoxidation reactor, oxygen and other impurities are removed utilizing the deoxidation process of the present invention. Alternatively, the deoxidation step may precede the NOx reduction step. Furthermore, these steps may be performed multiple times in any order. The NOx reduction step and the deoxidation step may be performed in a single reactor having a plurality of catalyst layers,
It may also be carried out in a single reactor with multiple chambers. In addition, each of the NOx reduction step and the deoxidation step may be performed using a plurality of reactors. This is,
The NOx reduction step is before the deoxidation step.

The recovery rate of nitrous oxide from nitrous oxide gaseous waste using this purification system is
Includes recoveries of greater than 50%, preferably greater than 70%, and more preferably greater than 95%.

EXAMPLES The methods of the present invention are further defined by reference to the following illustrative examples.

Example I The method for purifying nitrous oxide gas of the present invention is carried out as follows: 0.2% by weight on alumina in bead form from Johnson-Matsey.
The Pd catalyst is exposed at 150 ° C. in a quartz reactor to a gas flow of 60 cc / min consisting of 2.4 cc / min oxygen, 36 cc / min nitrous oxide and 6 cc / min helium. The contact time is 4.6 seconds. A portion of the helium gas is gradually replaced with pure hydrogen. By analysis of the reactor effluent by mass spectrometry (32 atomic mass units for oxygen, 28, 30 and 44 atomic mass units for nitrous oxide, 2 atomic mass units for hydrogen, 18 atomic mass units for water). , Follow up the reactor. In all cases tested, complete reaction of hydrogen is observed. 1 and 2 illustrate that oxygen selectively reacts with hydrogen and not selectively with nitrous oxide, respectively. FIG. 1 shows oxygen decomposition as a function of hydrogen flow. FIG. 2 shows% nitrous oxide decomposition as a function of hydrogen flow. FIG. 3 represents the oxygen decomposition selectivity as a function of hydrogen flow.

Example II The same experiment is carried out at 25 ° C., a contact time of 0.7 seconds and the same gas flow composition and velocity. Figures 4 and 5 show the performance achieved in this set of conditions. FIG. 4 shows oxygen decomposition as a function of hydrogen flow. FIG. 5 illustrates the% nitrous oxide decomposition as a function of hydrogen flow. FIG. 6 shows the oxygen decomposition selectivity as a function of hydrogen flow.

Example III The same experiment is carried out at 25 ° C., contact time 0.7 sec, with the same gas flow composition and velocity,
Part of the hydrogen is replaced by CO (ie 50% by volume or less CO). The oxygen decomposition and selectivity results are similar to those obtained with pure hydrogen.

Example IV The method for purifying nitrous oxide gas of the present invention is carried out as follows: CRI Catalyst Company, Inc. Commercially available grade S-096 SCR catalysts supplied by CO2 in an isothermal pipe reactor heated by a sand bath at an inlet temperature of 247 ° C., NOx 3%, O ₂ 8.0%, N ₂ O 26.5%, CO.
15 slpm containing 1%, 2% organic impurities (on a carbon basis) and the balance inerts
Exposing to adipic acid gas waste stream. The space velocity is 15,000 h ^-1 .
Ammonia is supplied stoichiometrically to the NOx level measured by the online NOx analyzer. The outlet composition is as follows: NOx 0.044%, O ₂ 7.3%, N ₂ O 26.5%, CO 0.2%, organic impurities 0.008% (on a carbon basis), residual inerts. .

[Brief description of drawings]

[Figure 1]   Figure 3 shows oxygen decomposition as a function of hydrogen flow.

[Fig. 2]   Shows% nitrous oxide decomposition as a function of hydrogen flow

[Figure 3]   Represents oxygen decomposition selectivity as a function of hydrogen flow.

[Figure 4]   Figure 3 shows oxygen decomposition as a function of hydrogen flow.

[Figure 5]   The% nitrous oxide decomposition as a function of hydrogen flow is illustrated.

[Figure 6]   Shows the oxygen decomposition selectivity as a function of hydrogen flow.

[Procedure for Amendment] Submission for translation of Article 34 Amendment of Patent Cooperation Treaty

[Submission date] June 1, 2001 (2001.6.1)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Contents of correction]

[Claims]

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, SD, SL, SZ, TZ, UG, ZW ), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, C R, CU, CZ, DE, DK, DM, EE, ES, FI , GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, K Z, LC, LK, LR, LS, LT, LU, LV, MA , MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, S K, SL, TJ, TM, TR, TT, TZ, UA, UG , UZ, VN, YU, ZA, ZW (72) Inventor Otzpenheim, GD P             Penns, Florida 32501, USA             Sacola, Port Royal Way 13 (72) Inventor Noskov, Alexander Stepanovitz             Chi             Russia, Novosibirisk 630090, Pi             -R Tetsutonoi 9-14 (72) Inventor Chindra Sekar, Lamor Tay             United States, South Carolina             29650, glia, birch leaf rain             100 (72) Inventor Claus, Gretz             California, United States, 94521,             Concord, Dayabelli Court 4490 F-term (reference) 4G069 AA03 BA01B BA04A BB04A                       BC54A BC72A BC72B BC75A                       CB81 DA06 EA02Y

Claims (30)

[Claims] 1. Feeding nitrous oxide gas and a reducing agent into a deoxidation reactor;
By reacting the reducing agent with the oxygen using a deoxidizing catalyst to reduce the oxygen in the nitrous oxide gas while limiting the amount of nitrous oxide removed from the nitrous oxide gas. A method for purifying nitrous oxide, which comprises deoxidizing to an inactive substance. 2. The method of claim 1, wherein the reducing agent comprises a hydrogen containing gas, a carbon monoxide containing gas or an ammonia containing gas. 3. The method of claim 1, wherein the reducing agent is a hydrogen containing gas. 4. The method of claim 1, wherein the inert material comprises water, carbon dioxide or nitrogen. 5. The method according to claim 1, wherein the inert substance is water. 6. The method of claim 1, wherein the nitrous oxide gas comprises NOx, nitrogen, carbon monoxide, carbon dioxide or an organic compound. 7. The NOx is removed from the nitrous oxide gas by selective catalytic reduction using ammonia or a precursor thereof and a selective catalytic reduction catalyst.
The method of claim 6. 8. The method of claim 6, wherein the carbon monoxide and organic compounds are removed from the nitrous oxide gas during the deoxidation. 9. The method of claim 1, wherein the nitrous oxide gas comprises adipic acid gaseous waste. 10. The gaseous waste comprises between 1000 ppm by volume and 10% by volume of oxygen and between 100 ppm by volume and 1% by volume of NOx.
The method described in. 11. The method of claim 1, wherein 99% by volume or less of oxygen is removed from the nitrous oxide gas. 12. The method of claim 1, wherein the deoxidation catalyst comprises palladium, platinum or mixtures thereof. 13. The method of claim 7, wherein the selective catalytic reduction catalyst comprises vanadium oxide, titanium oxide, or a mixture thereof. 14. The deoxidation step is carried out using one or more reactors,
The method of claim 1. 15. The method according to claim 7, wherein the selective catalytic reduction is performed in a selective catalytic reduction reactor separate from the deoxidation reactor. 16. The method of claim 15, wherein the selective catalytic reduction reactor is a lateral flow reactor. 17. The method according to claim 7, wherein steam is used as a carrier gas for the nitrous oxide gas during the selective catalytic reduction. 18. The method of claim 7, wherein an oxygen-containing gas is passed over the selective catalytic reduction catalyst before or after the selective catalytic reduction. 19. Feeding nitrous oxide gas and ammonia or precursor thereof to a reactor system; reacting said ammonia or precursor thereof with NOx in said nitrous oxide gas using a selective catalytic reduction catalyst. Performing selective catalytic reduction by; supplying a reducing agent to the reactor system; and performing deoxidation by reacting the reducing agent with oxygen in the nitrous oxide gas using a deoxidizing catalyst. A method for purifying nitrous oxide gas, comprising: 20. The method of claim 19, wherein the nitrous oxide gas comprises NOx, nitrogen, carbon monoxide, carbon dioxide or an organic compound. 21. The reactor system of claim 1, wherein the reactor system comprises one or more reactors.
9. The method according to 9. 22. The method of claim 19, wherein the deoxidation catalyst comprises palladium, platinum or mixtures thereof. 23. The method of claim 19, wherein the selective catalytic reduction catalyst comprises vanadium oxide, titanium oxide, or a mixture thereof. 24. The method of claim 19, wherein the selective catalytic reduction reactor is a lateral flow reactor. 25. The method of claim 19, wherein steam is used as a carrier gas for the nitrous oxide gas during the selective catalytic reduction. 26. The method of claim 19, wherein an oxygen-containing gas is passed over the selective catalytic reduction catalyst before or after the selective catalytic reduction. 27. The method of claim 19, wherein the recovery of nitrous oxide from the nitrous oxide gas using the reactor system comprises a recovery of greater than 95%. 28. Feeding nitrous oxide gas and ammonia or a precursor thereof to a reactor system; using a selective catalytic reduction catalyst while limiting the amount of nitrous oxide removed from said nitrous oxide gas. A method for purifying nitrous oxide gas, comprising performing selective catalytic reduction by reacting the ammonia or its precursor with NOx in the nitrous oxide gas. 29. The method of claim 28, wherein the nitrous oxide gas comprises NOx, nitrogen, carbon monoxide, carbon dioxide or an organic compound. 30. The method of claim 28, wherein the organic compound is selectively removed from the nitrous oxide gas stream by the selective catalytic reduction.